Heat-sensitive layer



g 11, 1959 T. v. CREVLlNG-ETAL 2,899,334

THERMOGRAPHIC COPYING MATERIAL Filed May 19, 1958 QU/NONE HEAT-SENSITIVE LAYER DIHYDROXYBENZENE SUPPORT Fig. 2

W' LAMP FACSIMILE (DARKENED PORTIONS) ll m LAYER Ill/mm PRINTED CHARACTER ORIGINAL Thomasvfl'revling Donald JIH act? 'I'homasLAbb INVENTORS mo mm THERMOGRAPHIC COPYING MATERIAL Thomas V. Crevling, Donald J. Haag, and Thomas I. Abbott, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Application May 19, 1958, Serial No. 736,248

9 Claims. (Cl. 117--36) This invention relates to thermographic copying material and to a method of using the same.

Thermographic copying materials and methods have been previously described in a number of domestic and foreign patents. These materials frequently have the' 'ad-' vantage of simplicity over certain photographic processes in that they produce a direct positive image of'the original upon exposing the heat-sensitive or thermographic copying mater'ial'to radiant energy (e.g., infrared radiation). However, certain of these thermographic materials which have been previously used are only slightly sensitive to heat, and, consequently, prolonged exposures are necessary in order to produce a facsimile copy. Other materials may not suffer from'the aforementioned defect, but theyare difficult to use, or handle, in that they contain metallic'ions which might stainthe'material upon which the heat-sensitive layer is coated. Other thermographic or heat-sensitive materials have the disadvantage of being excessively sensitive to ordinary light, and hence these materials must be handled in the dark until'they are first exposed to the graphic original. Other heatsensitive, copying materials exhibit thermotrophy and lose their developed color when the heat-sensitive material is cooled to room temperature. It is immediately obvious that these heat-senstive materials have onlylimited use, and, in certain instances, cannot be used at all if one desires to produce facsimile copies on a commercial scale.

The instant invention provides a convenient means of reproducing originals by exposure thereof in contact with certain heat-sensitive layers. The materials useful in our invention comprise a p-quinone compound and a dihydroxybenzene compound. We have found that when these compounds are maintained in physically-distinct relationship but in chemically-interactive relationship, they react with one another when exposed to radiation (e.g., infra-red) to an original, which contains certain areas highly absorptive of such radiation, so that those portions of the heat-sensitive material in contact with the portion of the original absorptive of such radiation, undergo a rapid color change. The color change produced according to our invention becomes more obvious as the heat-sensitive material cools to ambient temperature. In some instances, the heat-sensitive layers of our invention exhibit a reverse form of thermotrophy in that the color originally produced can be made to disappear upon heating the heat-sensitive layer, although the color returns once the heat-sensitive layer is cooled to room temperature.

Our invention is briefly illustrated in the accompanying drawings, wherein Fig. 1 is a graphic reproduction of a heat-sensitive, copying sheet which can be processed according to our invention, while Fig. 2 is a graphic reproduction of one method of ex posing the heat-sensitive, copying material of our invention in heat-conductive association with an original.

The two components forming the heat-sensitive areas of the copying sheets of our invention can be coated on any suitable support (especially supports having low thermal conductivity). in general, ordinary paper can be used as a support for the heat-sensitive composition and the paper can be transparent, translucent or opaque. Of course, it is frequently desirable to use a support which transmits the exposing radiation, especially where the original does not transmit such radiation (i.e., at least one of these should transmit such radiation). Advantageously, a paper or other fibrous material can be employed which has a charring temperature above about C.

The dihydroxybenzene compounds useful in practicing our invention comprise the hydroquinones, pyrocatechols, pyrogallols, etc. These dihydroxybenzenes can contain one or more of the conventional substituents of the type common in organic chemistry. We have found that these substituents do not generally interfere with the colorforming reaction upon which the instant thermographic process depends. A particularly useful group of dihydroxybenzene compounds comprisesthose represented by the following general formula:

1| R RP wherein R and R each represents a hydrogen atom, an alkyl group (e.g., methyl, ethyl, n-propyl, isopropyl', n-butyl, isobutyl, tert.-butyl, n-amyl, isoamyl, tert.-amyl, n-hexyl, isohexyl, 2-ethy1butyl, n-octyl, isooctyl, tort.- octyl, n-nonyl, n decyl, n-lauryl, n-hexadecyl, sec.-hexadecyl, n-octadeoyl, etc.), an alkenyl group (e.g., allyl', crotyl, etc.), a halogen atom (e.g., chlorine, bromine, etc.), a hydroxyl group, an acyl group (e.g., acetyl, butyryl, caprylyl', palmitoyl, etc.) an acyloxyl group (e.g., acetoxyl, benzoxyl, etc.) a carbamyl group (e.g., carbamyl, N-ethylcarbamyl, N-methylcarbamyl, N-Z-aminoethylcarbamyl, etc.), or an aryl group (e.g., phenyl, p-chlorophenyl, p-nitrophenyl, 0-, n-, or p-tolyl, etc.), R represents a hydrogen atom, or R and R together represent the groups necessary to complete a benzene ring (which can contain simple substituents, such as methyl, ethyl, hydroxyl, bromine, chlorine, etc.).

The p-quinone compounds which have been found to be especially useful in practicing our invention include those represented by the following general formula:

ethylcarbamyl, etc.), or an aryl group (e.g., phenyl, p-chlorophenyl, p-nitrophenyl, o-, n-, or p-tolyl, etc.),"

R represents a hydrogen atom, or alternatively, R and R together represent the groups necessary to form a benzene ring (which can contain simple substituents, such as methyl, ethyl, hydroxyl, bromine, chlorine, etc.).

The heat-sensitive layers useful in our invention can be prepared in several Ways, depending upon the use to which the-heat-sensitive,-copying sheet is to be put. In its simplest form, the invention contemplates the application of a solution of either the p-quinone compound or the dihydroxybenzene compound to the support, followed by evaporation of the solvent from the coating solution. Then a second solution is applied over the layer containing the first component of the heat-sensitive material and the solvent evaporated from this second coating solution. Advantageously, at least the second of the solvents is selected so that only one of the heat-sensitive components is soluble in that solvent, or the first component has too low a solubility to cause any harmful effect. For instance, a solution of the dihydroxybenzene compound in acetone can be applied to a translucent paper support and the acetone evaporated, after which a solution of the p-quinone compound in a solvent, such as trichloroethylene, is applied, followed by evaporation of this latter solvent. In addition to the aforementioned solvents, other solvents which can be employed include methylethylketone, benzene, 1,4-dioxane, diethyl ether, n-hexane, pyridine, etc. In general, it is preferable to employ a solvent having a low boiling point so that it can be rapidly removed from the coating.

The following examples will serve to illustrate briefly the simplest form of our invention, wherein one of the heat-sensitive components is coated on a translucent support, after which the other component is coated on top of the first heat-sensitive component. After a period of drying, the heat-sensitive, copying sheet can then be placed in contact with an original containing line copy, such as type-written characters, and exposed to infra-red radiation. The portions of the original which are highly absorptive of the infra-red radiation convert said radiation to heat which is conducted to the copying material producing a rapid color change in those portions of the copying sheet which are in heat-conductive relationship with the original. The portions of the copying sheet, which are not in heat-conductive relationship with the original, transmit or reflect the infra-red radiation so that no color change occurs.

The following tabulation shows p-quinone and dihydroxybenzene compounds which are useful in practicing our invention, together with the color of the image produced upon exposure of the heat-sensitive, copying sheets containing them, which can be prepared according to the method described above. The compounds listed in the table are named either as hydroquinone compounds or p-quinone compounds, except in those cases bearing an asterisk. In these latter cases, the compounds are named as complete chemicals for purposes of convenience, i.e., they are not named as hydroquinone compounds having substituents in the positions indicated above.

Color of Hydro qumone p-Quinone image Z-Methyl-S-n-hexadecyl 2-methlyl-5-n-hexa- Blue ee 2, 5-Di-n-oetyl 2,5-Din-nonyl 2-n Lauryl 5-n 2,5-D i-n-lauryl n-Oetadecyl 2,5-Di-n-octy n-Octadecyl d do Purple. d Yellow. 2,5-di-n-octyl. o. n-octadecyl... Purple. n-octyl.. Do

Color of Example Hydroquinone p-Quinone image 17 Z-MethyH-n-hexadecylp-chlorophenyl Rat} agentu. do p-nitrophenyl Green.

2-Gl1loro-6-te1 -butyl 2,5diacetoxy Blue. 2,3-dichloro D0. 2-methyl-5-n-hexa- Do.

2,5-Di-tert.-oetyl. Do. 1,2,4,5 Tetrahydr xy Do.

benzene.* Trimethyl Do. 2-Allyl-5-tert.-butyl Do. N (2 Aminoethy Do.

gentisamide.* 1,2,4,5 Tetrahydroxy 2,5diacetoxy Do.

benzene. Trimethyl do Do. 4,4- Dimethyl 2,2,5,5- 3,4-di-p-ehrophenyl.- Do.

tetrahydroxybiphenylf 30 2-Methyl-5-n-hexadecyl 1,4-naphthoqu1none*.- Red. 31 Phenyl 2-rnetl1yl-5-n-hexa- Purple decyl.

n-octadecyl Blue. n-octyl Do. 2,5-di-tert.-amyl Do. 2,5-di-n-lauryl Do. 2n'lauryl-5-n-amylnfl Do. 2,5-di-n-nonyl Do. n'laury Do. n-octadecyl Do. 2,5di-n-octyL- D0. 2,5-dl-n-lauryl. Do. 2-n-lauryl-5n-amylu Do. 2,5-di-n n0nyl Do. 44 rln n-laury D0. 45 2,6-Di'n-oetyL 2,5-din-octy1 D0. 30 46 do n-octadecyl Do. 47 rln n-octyl D0. 48 do 2, fi-di-n-lauryl Do. 2-n'lauryl-5-n-amyl" D0. 2, 5-di-n-nonyl..- Do. 2, 5 di n-oetyl- D0. D0. n-octy Do. 2, 5-di-tert.-amyl Do. tetrarnethyl Do. 2-n-lauryl-5n-amyl. Do. 2, fi-di-n-nonyL. Do. n-laur Do. 2, 5dl-n-octyl- Do. n-octadecyl. Do. 2-n-lauryl-5-n-amyl. D0. 2, 5-di-n-lauryL. Do. 2, 5'di-noctyl. Do. n-octadeeyl. Do. n-oct Do. 2, 5-dl-tcrt.-amyl Do. 2, 5 di-n-lauryl" Do. tetramethyL. D0. 2, fi-di-n-nony D0. n-lauryl Do. 2, 5-di-n-octyl. D0. n-octadecyl. Do. n-octyl D0. 2, 5-di-n-lauryl Do. tetrarnethyl Do. 2-n-lauryl-5-namyl. Do. n-laury Do. See.-0ctatlecyl n-octadecyl Do. .d n-oct Do. 2, 5-di-n-lauryl. Do. 2, 5-di-n-octyl. Do. -do n-octadecyl- Do. do n-octyl Do. 2, fi-di-n-lauryL. Do. do Z-n-lauryl-S-u-amyl. Do. 86 d 2, 5-dl-n-nonyl Do. 87 4-Phenyleatech0l zmethyl-en- Do.

hexadecyl. 88 Pyrogallol* do. Do. 89 2-Methyl-5-n- 1.. plus 2-methyl-5-npalmltyl.

METHOD A The p-quinone compound can be melted and then dispersed in a hot colloidal solution, such as a gelatin solution, using a solvent for the p-quinone compound, The dihydroxybenzene compound can then be dissolved in a suitable solvent, such as acetone, and this solution mixed with the dispersion containing the p-quinone compound and the mixture coated on a suitable support.

METHOD B The p-quinone compound can be ball-milled in an aqueous colloidal dispersion, such as a gum arabic dispersion. The dihydroxybenzene compound can likewise be ball-milled in the same type of colloidal dispersion, or a different type of colloidal dispersion, and the two dispersions-intermixed before coating on a suitable support.

METHOD C The p-quinone compound can be dissolved in a suitable solvent, such as chloroform, and this solution then dispersed in a colloidal solution, such as an aqueous gelatin solution, which is then dried, the solvent being evaporated off. A suitable dispersion of the dihydroxybenzene compound is made in a similar way, using a different solvent, such as butyl alcohol, and the solution then added to a colloidal solution, such as an aqueous gelatin solution, and the solvent evaporated off. The two dried dispersions can then be re-dispersed in water and combined and coated on a suitable support.

METHOD D In some cases, it is possible to melt the dihydroxybenzene compound and the p-quinone compound together at an elevated temperature, e.g., 90 C. The mixture can then be slowly added to a meltedcolloidal solution, such as an aqueous gelatin solution, maintained at a lower temperature, e.g., about 60 C., and then thoroughly dispersed by passing through a colloid mill. The resultant dispersion of the two components can then be coated on a suitable support. This method is possible in some cases, since one component crystallizes before the other to form two sets of separate, distinct particles dispersed in the colloid phase.

Colloidal materials which are suitable as binding agents for the heat-sensitive components of our invention include ethyl cellulose, polyvinyl alcohols, gelatin, collodion, polyvinyl acetals, cellulose esters, hydrolyzed cellulose esters, etc. The following examples illustrate the use of such binding agents in preparing heat-sensitive, copying sheets.

Example 90 Solution A.7.0 g. of 2-methyl-5-nhexadecylhydroquinone were ball-milled in 0.6 g. of ethyl cellulose and 60 cc. of trichloroethylene.

Solution B.-7.0 g. of 2-methyl-5-n-hexadecylquinone were dissolved in 30 cc. of trichloroethylene.

Solution B was then added to solution A and the mixture dispersed in 150 cc. of a 1% aqueous gelatin solution containing 1.5 cc. of a aqueous solution of a dispersing agent, such as sodium isobutylnaphthalene sulfonate. The dispersion was then coated on a thin paper support and dried.

Exposure of the dried coating to a graphic original containing line copy produced a sharp image of excellent contrast. Apparatus suitable for such an exposure is shown in Miller U.S. Patent 2,740,895, issued April 3, 1956.

Example 91 5.0 g. of Z-methyl-S-n-hexadecylhydroquinone were dissolved in 0 cc. of acetone. The solution was then coated by dip-coating on a paper coating machine using a 0.5- inch air knife pressure to give a uniform distribution of materials. The coating was then dried until substantially all acetone had been removed.

5.0 g. of Z-methyl-S-n-hexadecylquinone were dissolved in 100 cc. of trichloroethylene and the solution added to 50 cc. of a 5% (by weight) solution of ethyl cellulose in 6 trichloroethylene. The mixture was coated over the dried layer containing the hydroquinone, by a dip-coating technique using a 0.5-inch knife pressure to obtain uniform coating.

The resulting coating, after drying, had a very faint yellow color. Exposure of the coating to a printed letter by reflex on a thermographic copying machine of the type shown in U.S. Patent 2,740,895 gave an excellent reproduction having good blue color with low yellow D- min. A birefiex exposure made in the same manner also gave a good reproduction, but not as sharp as the reflex exposure. The temperature required to bring about the thermographic reaction was about 86 C.

Example 92 4.0 g. of 2methyl-5-n-hexadecylhydroquinone were combined with 45 cc. of trichloroethylene and the solution added to 25 cc. of a 5% ethyl cellulose solution in trichloroethylene. The resultant dispersion was ball-milled for 18 hours to give a fine slurry of the hydroquinone compound. A solution of 4.0 g. of 2-methyl-5-n-hexadecylquinone in 10 cc. of trichloroethylene was added to the fine slurry.

Coatings were prepared from the above dispersion by absorbing a portion thereof into a cotton swab and wiping onto Fidelity Bond Onion Skin paper. After drying, the coating had a very faint yellow color. Birefiex exposure of the dried coating to a printed letter gave an excellent copy wherein the facsimile portions were blue in color. The copy was right-reading.

The 'dihydroxybenzene compounds or the p-quinone compounds useful in practicing our invention comprise a large number of compounds which have been previously described in the literature. We have found that at least one of these compounds should melt or be fusible at a temperature within the range of about 55 to 125 C. Normally, the quinone compounds useful in practicing our invention will have a melting point of less than C., although it is to be understood that higher melting quinone compounds can be employed, particularly in those cases where the dihydroxy'benzene compound melts at a temperature below C.

Our invention can be further illustrated by reference to the accompanying drawing in which Fig. 1 is a crosssectional view of a thermographic copying material suitable for use in our invention. In Fig. 1, a support 10 is coated with a heat-sensitive layer 11 having dispersed therein a dihydroxybenzene compound 12 and a p-quinonne compound 13.

In Fig. 2, there is illustrated an assembly suitable for producing facsimile copies using the thermographic copying material of our invention. In Fig. 2, a graphic original 15, having printed material 14 thereon, is placed in contact with the uncoated surface of a support-10, having coated thereon a heat-sensitive layer 11. Upon exposure of the assembly to infra-red radiation supplied by an infra-red lamp 17, a fascimile copy of the printed characters of the original is reproduced in darkened portions 16.

If desired, the source of infra-red radiation can be arranged so that the rear surface of the original receives the infra-red radiation, although in such cases it may be convenient to have an insulating surface applied to the rear surface of the original in order to localize and intensify the heat received by the original. Alternatively, the heat-sensitive layer of the copying material can be placed in contact with the printed characters of the original (i.e., 14 of the drawing), and the assembly then exposed either from the side of the original or the rear side fo the copying sheet. These adaptations are well understood by those skilled in the art and are illustrated in domestic and foreign patents. See, for example, Miller U.S. Patent 2,663,657, issued, December 22, 1953.

the proportions of the dihydroxybenzene compound to the p-quinone compound can be varied, depending upon the effects desired. Equimolar quantities may be used in many instances, although an excess of one component may give improved results in some instances. Also, when acolloidal binding agent is employed, the amount thereof used may be varied in order to vary the contrast of the resulting copy. These effects are well understood by those skilled in the art. Various esthetic effects may be produced by adding inert pigments or colorants to the colloidal dispersions, although there is generally no advantage to be gained by the use of such materials. In some instances, an apparent increase in contrast can be obtained by using a coloring pigment in the colloidal binding material.

The p-quinone compounds useful in practicing our invention can be prepared by oxidation of the corresponding dihydroxybenzene compounds. Suitable oxidizing agents comprise a mixture of sodium chlorate and vanadium pentoxide, dichromic acid, etc. The preparation of typical quinone compounds useful in practicing our invention are illustrated in the following examples:

EXAMPLE A.2-METHYIr5-N-HEXADECYLQUINONE (2-N-HEXADE CYIr -l\IETHYLQUINONE) To a five-liter flask, equipped with an electric mantle, mechanical stirrer, thermometer and condenser, were added 2700 cc. of glacial acetic acid, 690 cc. of 2% sulfuric acid, 29.8 g. (0.28 mole) of sodium chlorate and 1 g. of vanadium pentoxide as catalyst.

With vigorous stirring, 174 g. (0.5 mole) of 2-n-hexadecyl-5-methylhydroquinone were added rapidly in portions, the temperature being held at 80 C. Stirring was continued at this temperature for one hour and for another hour without heat being applied.

The mixture was chilled under tap water and dried overnight at room temperature. The yield of crude quinone was 160.5 g. (92.5%), M.P. 80-83" C. This material was recrystallized by dissolving in 800 cc. of hot ligroin, filtration while hot, chilling under tap water, filtration and washing with cold ligroin. The final yield of 2-n-hexodecyl-5-methylquinone was 100.1 g. (57.5%), M.P. 8687 C.

EXAMPLE B.N-OCTADECYLQUINONE In a 20-gallon crock equipped with a copper cooling coil, dropping funnel and stirrer, were placed 48 l. of acetone and 2400 cc. of water. This solution was cooled to C. by passing 40 F. water through the coil. A 798-g. portion (2.2 moles) of n-octadecylhydroquinone was dissolved in the solution. The coil was removed, and 1100 ml. of concentrated sulfuric acid were added dropwise. This was followed by dropwise addition of a solution of 328 g. 1.1 moles) of sodium bichromate in 1100 ml. of concentrated sulfuric acid.

The blue-green slurry was stirred for minutes and an equal volume of water was added. The crystals were collected on two Lapp funnels and washed with two 600.

ml. portions of water. The damp crystals were recrystallized from 16 l. of ethyl alcohol and air dried to yield 765 g. (96%) of pale yellow plates; M.P. 86-87 C.

The dihydroxybenzene compounds useful in practicing our invention can be prepared according to methods which have been previously described in the literature. Many of these compounds are well-known. Methods of preparing such compounds have been previously described, for example, in Loria et al. US. Patent 2,728,- 659, issued December 27, 1955; Thirtle et al. U.S. Patent 2,732,300, issued January 24, 1956, etc. The following examples described the preparation of typical dihydroxybenzene compounds.

EXAMPLE C.-2-METHYL-5-PALMITOYLHYDROQUINONE +CH3(CH ;COOH

1120 K DHEI A one-liter, three-necked flask equipped with a stirrer, a gas inlet tube reaching near the bottom of the flask, and a gas outlet tube to the hood, was charged with a mixture of 62 g. (0.5 mole) of toluhydroquinone, 192 g. (0.75 mole) of palmitic acid, and 325 cc. of s-tetrachloroethane. Boron trifluoride was introduced with stirring for five hours; little heat was evolved and nearsolution resulted. After standing overnight, the reaction mixture was treated with more boron trifluoride for one hour while stirring and heating on a steam bath, then heated with stirring for eight hours longer.

The reaction mixture was allowed to stand overnight and was then poured into a solution of 205 g. of sodium acetate in 2 liters of water. Mechanical stirring gave a yellow paste under the aqueous layer. The latter was decanted and the paste stirred with 1250 cc. of petroleum ether until a thick slurry resulted (ca. 15 min.). The solid was collected on an 18.5 cm. Biichner funnel and washed with 500 cc. more petroleum ether, followed by 2 liters of water. The material, dried in a steam cabinet at 40 C., weighed 137 g. (75.7%) and contained some inorganic material. Recrystallization from 2400 cc. of ethyl alcohol diluted with 600 cc. of water gave pale yellow needles which were collected and washed with a mixture of 400 cc. of alcohol and cc. of water. The yield was 124 g. (68.5%), M.P. 9494.5 C. with a little softening at 91 C.

EXAMPLE D.2-CAPRYLYL-S-N-OCTYLHYDROQUINONE CO(CH2)o a +1120 CH3(CH2)5CH A one-liter, 3-necked flask was charged with a mixture of 111 g. (0.5 mole) of 2-n-octylhydroquinone, 108 g. (0.75 mole) of n-caprylic acid and 250 ml. of

s-tetrachloroethane. The flask was fitted with a gas inlet tube extending to the bottom of the flask, a thermometer, and gas outlet tube to the hood. The whole apparatus was counterpoised on a balance pan. Boron trifluoride from a cylinder was passed directly into the slurry at such a rate that the temperature was maintained at 40- 45 C. Considerable heat was evolved and the n-octylhydroquinone slowly dissolved to form -a dark, yellowbrown solution. When about 62 g. (0.9 mole) of boron trifluoride had been absorbed, which required about 1% hours, the addition was stopped. The outlet and inlet tubes were replaced by solid stoppers and the thermometer by an air condenser protected by a Drierite tube, and the flask was left at room temperature overnight (16-20 hours).

The flask was then heated on the steam bath for 6 hours. The mixture soon became turbid and drops of water were apparent in the upper part of the flask. At the end of the heating period, the mixture was cooled to room temperature and poured, with stirring, into a room temperature solution of 140 g. (1.7 moles) of sodium acetate in 1260 ml. of water. An additional 50 ml. of tetrachloroethane was used for rinsing out the reaction flask. The mixture was stirred at room temperature for about 30 minutes to complete the hydrolysis.

The organic layer was allowed to settle and was separated; the aqueous layer was extracted in a separatory funnel with two 500-ml. portions of ether. The ether extracts and the tetrachloroethane solution were combined, washed once with 250 ml. of water and then with four 250-ml. portions of 5% sodium carbonate solution. The at-first dark, yellow-brown solution became light-yellow on treatment with the carbonate. It was finally washed with 500 ml. of Water and dried'overnight over magnesium sulfate.

The filtered solution was concentrated under reduced pressure on the steam bath to a volume of about 300' ml. 600 ml. of petroleum ether were added and the mixture was cooled to The precipitate was filtered off, washed free of dark, oily material with petroleum ether, and dried in the air. It formed yellow crystals, M.P., 82-83 C., with some preliminary softening at 79 C. Weight: 115 g.

A second crop was obtained by concentrating the combined filtrate and washings under reduced. pressure. on the steam bath to complete removal of the solvents. The dark oily residue is treated with 300 ml. of petroleum ether and left overnight in the ice box. The solid was filtered off and washed with petroletun ether to give 13 g'. of yellow crystals, M.P. 81-82 C., softening at 77 C.

The combined crops (128 g.) were recrystallized from 640 ml. of cyclohexane, cooling the filtered solution overnight at about C. The precipitate was filtered ofi, washed with a little cold cyclohexane and then with three 100-ml. portions of petroleum ether. After drying in the air, the product formed light-yellow crystals, M.P. 8283 C. with slight softening at 80 C. Yield: 122 g. (70% of the theoretical 174 g.).

EXAMPLE E.2-ALLYL-5-TERT.-BUTYLHYDROQUINONE OCHz-CH=CH2 OH oHroH=oH,

can A o rr.

o'H OH A mixture of 180 g. (1109 moles) of tert.-butylhydroquinone, 92 g. (1.20 moles) of allyl chloride, 250 ml..of

'10 methanol, 50 ml. of water and 1 g. of zinc dust was heated to reflux under an inert atmosphere. A solution of 48 g. (1.2 moles) of sodium hydroxide in ml. of water was then added dropwise. The mixture was refluxed for 3 hours and was then cooled, diluted with 500 ml. of water and extracted with 500 ml. benzene.

The benzene solution was washed well with hot water and was then extracted with 5% aqueous sodium hydroxide to remove any unrecated tert.-butylhydroquinone. Distillationof the benzene solution gave 116 g. of material that boiled at 96l01 at 0.2 mm.

The above product was mixed with 300 ml. of kerosene (B.P. 215 C.) and the resulting mixture was refluxed for 2 hours. When cooled, a dark, mushy layer formed from which the kerosene was decanted. The dark product was extracted twice with 300-ml. portions of 25% acetic acid-water. Cooling the extract caused 23 g. of white, sticky crystals to separate. When crystallized from hexane-benzene and then from acetic acid-water, the product melted at l14-116 C.

Analysis.--Calcd. for C H O C, 75.72%; H,8.73%. Found: C, 75.75%; H, 8.93%.

EXAMPLE F.-2-CHLORO-5-TERT.-BUTYLHYDROQUI- NONE on on -o1 E +so2o1. +so.+no1 s-(jl- C r-(f CH3 CH3 i on on Charged 400 grams of chloroform to a 1000-ml. 3- necked, round-bottom flask fitted with a stirrer, thermometer, condenser and dropping funnel. The stirrer was started and 166 grams (1.0 mole) of mono-tertiary-butylhydroquinone were added. The mixture was heated to 48 C. and 141.5 grams (1.08 moles) of sulfuryl chloride were added from the dropping funnel over a threehour period at 48 C. Then 10 grams of Zinc dust were added and the mixture cooled to 10 C. The solids were filtered oil and the filtrate was extracted at 60 C. by adding 430. grams of 7% aqueous sodium hydroxide solution. The aqueous sodium hydroxide extract was cooled to 30 C., treated with 5 grams of sodium hydrosulfite and then made acid with concentrated hydrochloric acid. The light colored product was recovered by filtration and washed three times with cold water. The material was air dried to give 32 grams or 16% of theory of 2-chloro- S-tert.-butylhydroquinone, melting at -5 3 C.

In some instances, the dihydroxybenzene compounds can be prepared easily by reduction of the corresponding quinone compounds. This is illustrated in the following example:

EXAMPLE G.-1,2,4,5-TETRAHYDROXYBENZENE 3 6H Charged 250 grams of water, 70 grams (0.5 mole) of 2,5-dihydroxy-1,4-benzoquinone and 5 grams of 5% palladium (on alumina) catalyst to a 750-cc. stainless steel autoclave bowl. The bowl was mounted, the agitator started and the-system purged with nitrogen. The system was pressurized with 800 p.s.i. of-hydrogen and the reaction carried out at 800-1000 p.s.i. of hydrogen and at a temperature of 27-47 C. Heat was evolved and p.s.i. of hydrogen were taken up. The reaction mixture was heated to 72 C. and the system purged with nitro" gen. The contents were discharged at 70-80 C. into a beaker containing 25 grams of water, one gram of sodium hydrosulphite and 5 grams of decolorizing carbon. The

decolorizing carbon and catalyst were removed by filtration at 8085 C. through super cell. The clear filtrate was cooled with stirring to C. and the crystallized 1,2,4,S-tetrahydroxybenzene recovered by filtration. It was washed once with grams of cold water and dried in the dark at 6065 C. and 10-15 inches of vacuum. The yield of light grey solid, M.P. 220-25 C., was 45 grams or 64% of theory.

In Example 92 above, reference is made to a bireflex exposure. Such an exposure is illustrated in Figure 2 of the accompanying drawings. It can be seen by reference to Figure 2 that the support 10 for such an exposure should be readily permeable to the radiant energy, such as infra-red radiation. Also, the support is advantageously relatively thin so that the heat generated in the printed characters (14) can be transmitted to the heatsensitive layer 11, thereby causing a color change to take place in a pattern corresponding to the printed characters. If desired, the support 10 may consist of ordinary paper which has been transparentized temporarily, so that exposure can be made as described. The transparentizing substance can then be removed after exposure to provide an opaque reflecting support. Such transparentizing treatment is well known to those skilled in the art.

It has also been found that the application of the heat-sensitive layer to the support need not be done in a uniform manner, but that the heat-sensitive layer can be applied non-uniformly in a regular pattern, such as lines or dots. Such coatings can be used for special purposes, such as in the graphic arts field.

While the accompanying drawing illustrates an infrared lamp as the conventional exposing source, it is to be understood that other sources of radiant energy can conveniently be employed. Advantageously, the source of radiation is selected so that it is strongly absorbed by the characters or printed materials being reproduced. Thus, the characters absorb the radiant energy and transform it into heat which is transmitted to the heat-sensitive coating. Incandescent bodies can conveniently be employed as the source of radiant energy, since such incandescent material is generally rich in the radiant energy absorbed by many of the printing materials currently being used. Where the radiant energy is not transmitted by the support bearing the heat-sensitive material, the material being copied should transmit such radiant energy so that exposure can be made through the rear surface of the material bearing the printed characters.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. A heat-sensitive, copying sheet comprising a support and coated on said support a heat-sensitive area containing (a) a p-quinone compound and (b) a dihydroxybenzene compound, at least one of said compounds having a melting point between about 55 and 125 C., said compounds being maintained in physically-distinct relationship and in chemically-interactive relationship so that upon exposure of said heat-sensitive area to radiant energy in heat conductive association with a pattern containing portions highly absorptive of said radiant energy and portions substantially nonabsorptive of said radiant energy, said heat-sensitive area undergoes a rapid color change only in those areas in heat conductive association with those areas highly absorptive of said radiant energy, said heat-sensitive, copying sheet being stable at room temperature, being substantially insensitive to visible radiation and being non-sticking at 125 C.

2. A heat-sensitive, copying sheet comprising (1) a 12 fibrous support and (2) a heat sensitive colloid layer having dispersed therein (a) particles of a p-quinone compound selected from those represented by the following general formula:

ll a

wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a halogen atom, a hydroxyl group, an acyl group, an acyloxyl group, a carbamyl group, and an aryl group, R represents a member selected from the group consisting of a hydrogen atom and groups which together with R represent the atoms necessary to complete a benzene ring, and R when R represents a hydrogen atom, represents a member selected from the group con sisting of a hydrogen atom, an alkyl group, an alkenyl group, a hydroxyl group, a halogen atom, an acyl group, an acyloxyl group, and an aryl group, and (b) particles of p-dihydroxybenzene compound selected from those represented by the following general formula:

wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a halogen atom, a hydroxyl group, an acyl group, an acyloxyl group, a carbamyl group and an aryl group, R represents a member selected from the group consisting of a hydrogen atom and groups which together with R represent the atoms necessary to complete a benzene ring, and R when R represents a hydrogen atom, represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a hydroxyl group, a halogen atom, an acyl group, an acyloxyl group, and an aryl group, at least one of said compounds having a melting point between about 55 and C., said compounds being maintained in physically-distinct relationship and in chemically-interactive relationship so that upon exposure of said heat-sensitive area to radiant energy in heat conductive association with a pattern containing portions highly absorptive of radiant energy and portions substantially nonabsorptive of said radiant energy, said heat-sensitive area undergoes a rapid color change only in those areas in heat conductive association with those areas highly absorptive of radiant energy, said heat-sensitive, copying sheet being stable at room temperature, being substantially insensitive to visible radiation and being non-sticking at 125 C.

3. A heat-sensitive, copying sheet comprising (1) a thin paper support having low thermal conductivity and (2) a heat-sensitive colloid layer having dispersed therein (a) discrete particles of a p-quinone compound selected from those represented by the following general formula:

wherein R represents an alkyl group containing from 1 to 18 carbon atoms and R represents a member selected from the group consisting of a hydrogen atom and an alkyl group containing from 1 to 12 carbon atoms, and

13 (b) discrete particles of a dihydroxybenzene compound selected from those represented by the following general formula:

wherein R represents an alkyl group containing from 1 to 18 carbon atoms and R represents a member selected from the group consisting of a hydrogen atom and an alkyl group containing from 1 to 12 carbon atoms, at least one of said compounds having a melting point between about 55 and 125 C., said compounds being maintained in physically-distinct relationship and in chemically-interactive relationship so that upon exposure to infra-red radiation of said heat-sensitive area in heat conductive association with a pattern containing portions highly absorptive of infra-red radiation and portions substantially nonabsorptive of infra-red radiation, said heat-sensitive area undergoes a rapid color change only in those areas in heat conductive association with those areas highly absorptive of infra-red radiation, said heat-sensitive, copying sheet being stable at room temperature, being substantially insensitive to visible radiation and being nonsticking at 125 C.

4. A heat-sensitive, copying sheet as defined in claim 3, wherein the quinone compound is Z-methyI-S-n-hexadecyl-p-quinone and the dihydroxybenzene compound is Z-methyl-S-n-hexadecyl-hydroquinone.

5. A heat-sensitive, copying sheet as defined in claim 3, wherein the quinone compound is n-octadecyl-p- 14 quinone and the dihydroxybenzene compound is n-octadecylhydroquinone.

6. A heat-sensitive, copying sheet as defined in claim 2, wherein the quinone compound is 2-methyl-5-n-hexadecyl-p quinone and the dihydroxybenzene compound is 2-methyl-5-palmitoylhydroquinone.

7. A heat-sensitive, copying sheet as defined inclaim 3, wherein the quinone compound is 2,5-di-n-octyl-p quinone and the dihydroxybenzene compound is n-octylhydroquinone.

8. A heat-sensitive, copying sheet as defined in claim 3, wherein the quinone compound is Z-methyl-S-n-hexadecyl-p-quinone and the dihydroxybenzene compound is 2,S-di-n-octyl-hydroquinone.

9. A heat-sensitive, copying sheet comprising a support and coated on said support a heat-sensitive area containing (a) a p-quinone compound and (b) a dihydroxybenzene compound, at least one of said compounds having a melting point between about and C., said compounds being maintained in physically-distinct relationship and in chemically-interactive relationship so that upon exposure of said heat-sensitive area to radiant energy in heat conductive association with a pattern containing portions highly absorptive of said radiant energy and portions substantially nonabsorptive of said radiant energy, said heat-sensitive area undergoes a rapid color change only in those areas in heat conductive association with those areas highly absorptive of said radiant energy, said heat-sensitive, copying sheet being stable at room temperature, being substantially insensitive to visible radiation and being non-sticking at 125 C., said pquinone compound being present in a separate layer and distinct from a layer comprising said dihydroxybenzene compound.

No references cited. 

1. A HEAT-SENSITIVE, COPYING SHEET COMPRISING A SUPPORT AND COATED ON SAID SUPPORT A HEAT-SENSITIVE AREA CONTAINING (A) A P-QUINONE COMPOUND AND (B) A DIHYDROXYBENZENE COMPOUND, AT LEAST ONE OF SAID COMPOUNDS HAVING A MELTING POINT BETWEEN ABOUT 55 AND 125*C., SAID COMPOUNDS BEING MAINTAINED IN PHYSICALLY-DISTINCT RELATIONSHIP AND IN CHEMICALLY-INTERACTIVE RELATIONSHIP SO THAT UPON EDPOSURE OF SAID HEAT-SENSITIVE AREA TO RADIANT ENERGY IN HEAT CONDUCTIVE ASSOCIATION WITH A PATTERN CONTAINING PORTIONS HIGHLY ABSORPTIVE OF SAID RADIANT ENERGY AND PORTIONS SUBSTANTIALLY NONABSORPTIVE OF SAID RADIANT ENREGY, SAID HEAT-SENSITIVE AREA UNDERGOES A RAPID COLOR CHANGE ONLY IN THOSE AREAS IN HEAT CONDUCTIVE ASSOCIATION WITH THOSE AREAS HIGHLY ABSORPTIVE OF SAID RADIANT ENERGY, SAID HEAT-SENSITIVE, COPYING SHEET BEING STABLE AT ROOM TEMPERATURE, BEING SUBSTANTIALLY INSENSITIVE TO VISIBLE RADIATION AND BEING NON-STICKING AT 125*C. 